Torsion pendulums, which have oscillatory cycles on the order of tens of seconds, have been used in the art of chronometry for a long time. The large time constants of these torsion pendulums minimize their energy consumption so that spring-loaded clocks of this type can be operated for a long period without rewinding. In electrically powered clockworks their current consumption is minimal.
This low energy consumption, on the other hand, makes such a clockwork sensitive to impact timepiece; vibration and also requires a level base for the timpiece; thus, clocks of this type are liable to operate irregularly or to stop prematurely. Even with precision manufacture, they are difficult to calibrate properly in order to keep time with a reasonable degree of accuracy.
Nevertheless, timepieces with torsion pendulums have found wide public acceptance presumably due to the esthetic appeal and nerve-soothing effect of a pendulum weight oscillating with a slow rhythm about a vertical axis. The pendulum weight itself is usually of ornamental design, frequently comprising a pair of intersecting arms carrying metal balls at their ends.
Thus, it has already been proposed to equip a timepiece with a normal clockwork and a torsion pendulum. If the pendulum is provided with its own stepping mechanism independent of the functional clockwork, such as a Graham escapement, the timepiece becomes complex and correspondingly expensive. Earlier suggestions for an operative coupling between the clockwork and the torsion pendulum, however, entail various drawbacks. According to German published specifications Nos. 1,798,274 and 1,936,654, for example, the clockwork is controlled by an escapement of the sling-drive type whose oscillating weight acts upon the torsion spring of the pendulum through a coupling between that spring and the sling mounting. The interaction between two systems of different natural frequencies generates interference phenomena which may arrest the pendulum and also can adversely affect the operation of the clockwork itself, in the absence of special synchronization circuits as disclosed in the second one of these publications. A contactless magnetic coupling between the clockwork and the torsion pendulum, as described in German published specification No. 2,058,037, avoids some of these difficulties but requires a strong magnetic field in its practical realization, with a correspondingly bulky structure. Moreover, such magnetic couplings are not practical with electrodynamically driven clockworks which are susceptible of malfunction caused by stray magnetic flux and which therefore require high-precision workmanship.